Malignant counterpart: chordoma
The lesion is typically asymptomatic and may be first recognized on imaging studies.
Usual location: level of clivus or sacrum
Size: usually less than 6 mL; if > 6 mL termed giant
Imaging studies:
(1) hypointense on T1 and hyperintense on T2
(2) non-enhancing with gadolinium
(3) bony pedicle (stalk) with focal bone destruction
Histologic features:
(1) physalliphorous cells with large intracytoplasmic mucin-containing vacuoles in a myxoid amphophilic matrix
(2) hypocellularity
(3) absent or rare mitoses
(4) minimal pleomorphism
(5) absence of tumor necrosis
Immunohistochemistry:
(1) cytokeratin positive
(2) brachyury positive (encoded by TBXT gene)
(3) GFAP negative
(4) Ki67 less than 1%
